A change in the mechanism of food distribution has brought about an increasing demand for packaged foods. While packaged food is susceptible to deterioration in a variety of ways, depending upon conditions during distribution and storage, one of the most serious problems arises from spoilage due to oxygen. A wide variety of packaged foods are caused to deteriorate by oxidation since they are readily oxidizable. Oxidation causes changes in color and flavors, reduction in nutritional value, and other disagreeable conditions which give rise to complaints from consumers.
The changes in quality of packaged foods can also be caused by microorganisms. In order to prevent changes due to microorganisms or oxidation, it is customary to rely on food additives, such as antimicrobial and antimycotic agents and antioxidants.
Current methods for removing oxygen from packages are fraught with shortcomings:
1. Flushing with inert gases results in incomplete oxygen removal, particularly in the interior of porous foods. Furthermore, inert gas flushing provides no protection against subsequent oxygen influx. In order to flush with inert gases, the package interiors are evacuated and nitrogen or carbon dioxide gas is sealed in the evacuated package. Another problem with this method of preventing oxidative deterioration of foods is that an exact selection of combinations of articles to be packaged, and packaging material are required to achieve the intended results. Selection of favorable conditions for the methods demands a tremendous amount of time and data, and use of a high-efficiency packaging machine and a highly gas-impervious packaging material.
2. Vacuum packaging can only be used for certain foodstuffs, because some foodstuffs are likely to be deformed in the negatively pressurized interior of the package.
3. Coupled enzyme systems, such as glucose oxidase/peroxidase, undergo rapid inactivation and are very sensitive to changes in pH, water activity, solvent system, salt content, temperature, and various other factors. Additionally, these systems require the addition of water from the outside for their action, and therefore cannot be effectively used for low-water content foodstuffs, although they may work reasonably well with foodstuffs containing a great amount of water. These systems thus have limited practical utility.
4. Packages containing elemental iron remove oxygen by virtue of rusting, but at a very slow rate. Thus, this is impractical. This method is virtually ineffective below 0.degree. C., and therefore provides no protection against common oxidative freezer damage.
5. The removal of oxygen by hydrogen gas is expensive and burdensome. The material to be protected is packaged in a material of a laminated structure of a polyester/metal foil/Surlyn/palladium/Surlyn (trademark of ionomer by DuPont Company) by gas substitution with a mixture of hydrogen and nitrogen gases whereby oxygen remaining in the package is reacted with the hydrogen gas under the catalytic action of palladium in the laminate to permit elimination of oxygen.
Addition of an antioxidant, antiseptic, or any other like additives to foodstuffs, which has been extensively adopted for the purpose of preservation, has the disadvantage that a technically sufficient amount of additives is prohibited by various statutes and regulations concerning additives for foodstuffs, pharmaceuticals, or cosmetics in light or their adverse effects on the human body. In addition, known hazardous materials cannot be used for foods, pharmaceuticals, and cosmetics.
The sensitivity of ascorbic acid to copper-catalyzed oxidation was recognized immediately after this discovery by Szent-Gyorgyi in 1928, and its structural determination and chemical synthesis in 1933. During the past 50+ years, a multitude of studies were conducted to investigate the kinetics and thermodynamics of oxidation of ascorbic acid by transition metals such as copper and iron, and their various chelates.
Historically, trace amounts of copper (less than 0.1 ppm) have been known to catalyze oxygen radical formation and lipid peroxidation, leading to rapid food spoilage, especially of food susceptible to oxidative damage. Therefore, painstaking efforts are being made in several food areas, such as the diary industry, to eliminate all exposure of food to copper-containing equipment. Higher levels of copper are expected to aggravate this deteriorative effect of copper. Based on this current knowledge, the system of the present invention is not obvious and is contrary to conventional wisdom, since 5-7 ppm copper in the presence of a reducing agent, such as ascorbic acid, completely preserves oxygen-sensitive foods.
Nakamura et al., in U.S. Pat. No. 4,384,972, disclose an agent for maintaining the freshness of a packaged foodstuff comprising a salt of manganese (II), iron (II), cobalt (II), or nickel (II), an alkali compound, and a sulfite or deliquescent substance. Ascorbic acid or a salt thereof may optionally be included.
Siegel, in U.S. Pat. No. 3,320,046, discloses a formulation for conditioning cut flowers comprising an inorganic compound selected from the group consisting of water soluble inorganic salts or chelates which contain the one of the following metal ions: copper (II), zinc (II), manganese (II), cobalt (II), or nickel (II). The second component of the composition is ascorbic or isoascorbic acid, and the third component of the composition is an antioxidant such as a vinyl ether, an alkyl phenol, a phenolic ether, or the like.
Pottier, in U.S. Pat. No. 3,294,825, discloses an antioxidant composition for protecting lipids against oxidation comprising a combination of ascorbic acid and citric acid.
Stone, in U.S. Pat. No. 2,892,718, discloses a composition for treating malt beverages comprising sodium hydrosulfite and a salt of ascorbic acid.
Japanese patent No. 55-118344 discloses a method for preventing discoloration by immersing the vegetables in an aqueous solution containing an acid, a chelating agent such as sodium metaphosphate, and a harshness-removing agent such as burnt alum.